Effects of various articulatory features of speech on cortical event-related potentials and behavioral measures of speech-sound processing.

OBJECTIVE

To investigate the effects of three articulatory features of speech (i.e., vowel-space contrast, place of articulation of stop consonants, and voiced/voiceless distinctions) on cortical event-related potentials (ERPs) (waves N1, mismatch negativity, N2b, and P3b) and their related behavioral measures of discrimination (d-prime sensitivity and reaction time [RT]) in normal-hearing adults to increase our knowledge regarding how the brain responds to acoustical differences that occur within an articulatory speech feature and across articulatory features of speech.

DESIGN

Cortical ERPs were recorded to three sets of consonant-vowel speech stimuli (/bi versus /bu/, /ba/ versus /da/, /da/ versus /ta/) presented at 65 and 80 dB peak-to-peak equivalent SPL from 20 normal-hearing adults. All speech stimuli were presented in an oddball paradigm. Cortical ERPs were recorded from 10 individuals in the active-listening condition and another 10 individuals in the passive-listening condition. All listeners were tested at both stimulus intensities.

RESULTS

Mean amplitudes for all ERP components were considerably larger for the responses to the vowel contrast in comparison with the responses to the two consonant contrasts. Similarly, the mean mismatch negativity, P3b, and RT latencies were significantly shorter for the responses to the vowel versus consonant contrasts. For the majority of ERP components, only small nonsignificant differences occurred in either the ERP amplitude or the latency response measurements for stimuli within a particular articulatory feature of speech.

CONCLUSIONS

The larger response amplitudes and earlier latencies for the cortical ERPs to the vowel versus consonant stimuli are likely related, in part, to the large spectral differences present in these speech contrasts. The measurements of response strength (amplitudes and d-prime scores) and response timing (ERP and RT latencies) for the various cortical ERPs suggest that the brain may have an easier task processing the steady state information present in the vowel stimuli in comparison with the rapidly changing formant transitions in the consonant stimuli.